Ilias Miroslav, Saue Trond, Enevoldsen Thomas, Jensen Hans Jørgen Aa
Department of Informatics, Faculty of Management Science and Informatics, University of Zilina, Campus Prievidza, SK-97101 Prievidza, Slovakia.
J Chem Phys. 2009 Sep 28;131(12):124119. doi: 10.1063/1.3240198.
The use of perturbation-dependent London atomic orbitals, also called gauge including atomic orbitals, has proven efficient for calculations of NMR shielding constants and other magnetic properties in the nonrelativistic framework. In this paper, the theory of London atomic orbitals for NMR shieldings is extended to the four-component relativistic framework and our implementation is described. The relevance of London atomic orbitals in four-component calculations as well as computational aspects are illustrated with test calculations on hydrogen iodide. We find that the use of London atomic orbitals is an efficient method for reliable calculations of NMR shielding constants with standard basis sets, also for four-component calculations with spin-orbit coupling effects included in the wave function optimization. Furthermore, we find that it is important that the small component basis functions fulfill the magnetic balance for accurate description of the diamagnetic shielding and that the role of London atomic orbitals in the relativistic domain is to provide atomic magnetic balance even in the molecular case, thus greatly improving basis set convergence. The Sternheim approximation, which calculates the diamagnetic contribution as an expectation value, leads to significant errors and is not recommended.
使用依赖微扰的伦敦原子轨道（也称为含规范原子轨道）已被证明在非相对论框架下计算核磁共振屏蔽常数和其他磁性性质时是有效的。在本文中，用于核磁共振屏蔽的伦敦原子轨道理论被扩展到四分量相对论框架，并描述了我们的实现方法。通过对碘化氢的测试计算，说明了伦敦原子轨道在四分量计算中的相关性以及计算方面的问题。我们发现，使用伦敦原子轨道是一种有效的方法，即使在波函数优化中包含自旋轨道耦合效应的四分量计算中，也能使用标准基组可靠地计算核磁共振屏蔽常数。此外，我们发现，小分量基函数满足磁平衡对于准确描述抗磁屏蔽很重要，并且伦敦原子轨道在相对论领域的作用是即使在分子情况下也能提供原子磁平衡，从而大大提高基组收敛性。将抗磁贡献计算为期望值的施特恩海姆近似会导致显著误差，因此不建议使用。
